Flameholder configuration



Oct. 2, 1962 R. A. KRABACHER ETAL 3,056,261 FLAMEHOLDER CONFIGURATION Filed Sept. l, 1959 MALML n BShdl Patented ct. 2, 1962 ice 3,555,261 FLAMEHULDER CNlFiGURATlN Roy A.. Krabacher, Everett W. Waters, and Henry E. Kamps, Cincinnati, Gino, assignors to Genera Electric Company, a corporation of New Yerk Fiierl Sept. 1, 1959, Ser. No. 837,543 1 Claim. (C1. 611-3972) The present invention relates to a flameholder configuration for aircraft jet engine afterburners and more particularly to an improved tiameholder configuration in which thermal and gas load bending stresses are reduced to a minimum.

Up to the present time it has been the practice in designing llameholders for jet engines to provide one or more V-gutters which are rigidly supported in the turbine discharge passage of the engine between the structural shell of the engine tailpipe and the tailcone. Since the flame holder is suspended within the tailpipe it is exposed to the engine exhaust gases. The high velocity exhaust gases impinge directly on the V-gutters and supporting members and imposed aerodynamic loading stresses thereon. The wide temperature range of the exhaust gases causes differential expansion and contraction of the V-gutters, thus creating thermal stresses in the ameholder. ln conventional flameholder designs V-gutters and support members have been provided with rigid interconnections and massive cross-sections in order to resist the stresses imposed by the exhaust gases. Likewise, the tailpipe and tailcone have had to be of massive construction in order to resist the bending moments acting on the flameholder support members. In such designs, the effective operating life of the flameholder generally varies directly with the mass and weight of its components. This has presented a severe problem in the design of aircraft jet engines since weight is a critical factor of engine design.

An object of the present invention is to provide a flameholder configuration which is light and strong and has an increased effective life over heretofore known designs.

The above object is realized in the present invention by provision of a flameholder configuration which eliminates or reduces to a minimum the gas load bending stresses and torsional stresses in the flameholder rings and eliminates gas load bending stresses from the supporting members. This is accomplished by interconnection of the ameholder rings, support members and structural members of the engine by pin connections which allow the rings to expand and contract individually and which allow all tensile forces to be transmitted through the shear center of the ring cross-sections.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

AFIG. 1 is an elevation view partly in section of a portion of -a jet engine in which the present invention is installed;

FIG. 2. is an elevation view at an enlarged scale of the flameholder configuration of FIG. 1; and

IFIG. 3 is a schematic view of the flameholder configuration of the present invention showing the location and disposition of gas loads and tensile forces.

Referring more particularly to FIG. 1, the ameholder configuration of the present invention is shown as installed in a jet engine downstream of turbine wheels and 11, and within turbine discharge passage 12 which is defined by the engine tailpipe 13 and the tailcone 14. The ameholder configuration of the present invention is mounted on the tailcone 14 and includes three concentric flameholder rings 15, 15 and 17 interconnected by radial links 18 and 19. Another link 21 connects the flameholder assembly to a bracket ZG which is secured to the tailcone.

As shown in FIG. 2, each of the flameholder rings includes an upper and lower arm, 222 and 23, joined to a tubular member 24 which for-ms the apex of the V. A clevis connector 25- is secured to the tubular member of ring 16 and extends forwardly and downwardly therefrom. A similar clevis connector 26 is secured to the tubular member of ring 17 and extends forwardly and upwardly therefrom. A generally C-shaped clevis connector 27 is secured to the tubular portion of ring 15 and extends downstream thereof adjacent the upper and lower arms of the ring. Link 18 is secured to connectors 25 and 27 by means of pins 28 and 29. Link 19 is similarly secured to connectors 26 and 27 by pins 31 and 32. Short baiiies or arms 33 and 34tare secured to links 18 and 19 and project rearwardly and outwardly therefrom to arms Z2 and Z3 projecting from tubular member 242-. A clevis connector 35 is secured to the bracket 2f). Link 21 is connected to connectors 27 and 35 by means of pins 36 and 37.

Since, as illustrated in FIG. 2, the individual flameholder rings are pivotally connected to each other and to the structural member (tailcone 11i) they are each free to expand and contract individually. lf one of the llameliolder rings expands or contracts at a different rate, or to a different degree than another, it merely moves relative to the other ring. No stresses are transmitted from one to another by uneven expansion or contraction. Accordingly, thermal stresses due to differential expansion and contraction are avoided in the present flameholder configuration.

The use of links and pin-clevis connections allows the flameholders to be loaded in such a way that only tensile forces are transmitted between rings and between the fiameholder assembly and the structural member of the engine. By letting the line of action of each tensile force pass through the shear (flexural) center of the flameholder rings, the rings themselves are able to take the maximum structural loads without unnecessary secondary loading effects. Referring to FIG. 3, the aerodynamic drag load D is assumed to be equally distributed around the circumference of each of the fiameholder rings. Since radial links '1S and 19' are connected to liameholder rings 16 and 17 respectively by pins 28 and 31, tensile loads T1 and T2 are produced in the links. `lf the lines of action of the forces T1 and T2 pass through the shear centers of the cross-sections of the flameholder rings as shown, the torsional stresses at the support will be zero. The force distribution condition at ameholder ring 15 is also shown on PIG. 3. Since links 18 and 19 are pinned to connector 27 and since the lines of action of forces T1 and T2 pass through the shear center of ring 15, no torsional stresses are imposed upon ring 15 by rings 16 and 17. Link Z1 is similarly pinned to connector Z7 and the line of action of tensile force T3, which is produced in the link, passes through the shear centers of liameholder ring 15 and bracket Ztl. Accordingly, with the present flameholder configuration, no torsional stresses are developed in any one of the flameholder rings by the support system. This figure also serves to illustrate another advantage of the present llameholder configuration. The net radial load carried by link 21 is the result of the summation of forces T1 and T2. It should be noted that the radial components of these forces are in opposite directions, and that they accordingly subtract from each other. The stresses produced in the center ameholder ring are thus materially reduced over what would be the case if rigid connections were used and the loads were carried in bending.

The transmission of the forces due to aerodynamic drag loads through the shear centers of the flameholder rings add rigidity to the ring construction. In addition, the use `of a tubular member to form the leading `edge of the iiameholder ring `adds strength to the ring construction. The basic reasoning behind this feature is the development of the major ystrength section in a relatively cool 'area of the flameholder ring. Since the leading edge of the ring runs `at a much cooler temperature than the trailing edge, placing the supporting tube (which has high torsional rigidity) at the leading edge gives the advantage of having the major supporting member at the coolest temperature.

An additional feature `of the present flameholder contiguration, is the use of a pin-clevis connection between link 21 and tailcone 114. By means of this connection, the forces due to the aerodynamic drag loads on the flameholders `are transmitted to the tailcone in pure tension, thus eliminating any bending moment due to such loads.

In practice link 21 may be secured to the tailcone, the tailpipe, or to a transverse strut as long as the line of action of force T3 passes through the center of shear of lameholder ring 1S. In this connection the center of shear of the V-gutter configuration shown closely approaches the center of the tubular member. Accordingly, for all practical purposes the condition of no torsional stress can be achieved by having the lines of action of the tensile forces pass through the center of the cross-section of the tubular member.

Obviously many modiiications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the `scope of the appended claim, the invention may be practiced otherwise than as specifically described.

What is claimed is:

An afterburner ilameholder assembly for use in a jet exhaust pipe, said assembly comprising: a plurality of annular gutter members including iirst, second, and third ring members, said ring members being coaxial and of different diameters with said third ring member positioned intermediate of said first and second members; `and support means for said assembly including a first plurality of linking members pivotally interconnecting and locating said rst and second ring members relative to said third ring member, and a second plurality of linking members pivotally connecting and locating said `assembly relative to the pipe, wherein the lines of action `of the tensile forces developed in said pluralities `of linking mem-bers by impingement of the exhaust stream on said gutter members pass through the shear centers of said ring members, so that induced bending stresses in said linking members are eliminated and induced torsional stresses in said ring members are minimized.

References Cited in the tile of this patent UNITED STATES PATENTS 2,696,709 Oulianoif Dec. 14, 1954 2,714,287 Carr Aug. 2, 1955 2,726,511 Pitt Dec, 13, 1955 2,793,495 Karcher May 28, 1957 2,874,536 Benson Feb. 24, 1959 2,944,399 McCardle July 12, 1960 OTHER REFERENCES Cissel: Stress Analysis and Design of Elementary Structures, 2nd edition, I'ohn Wiley & Sons, Inc., 1948. 

